How Automotive Warning Lights Work

Are Automotive Warning Lights Accurate?

With all the sensors in the car trying to determine if there are any problems with the vehicle, how sure can a driver be that the warning lights are accurate? The quick answer is: you can be pretty sure.

Sometimes, a sensor may trigger the warning light to come on, but then it quickly goes off. Typically this occurs when the sensor has told the Engine Control Unit (ECU) of a problem, but doesn't notice the problem as reoccurring. When this happens, it doesn't mean that the system isn't working. It usually means that the system found a problem but that it's been corrected or isn't persisting. In either case, unless your owner's manual recommends you do so, it's not necessary to take your vehicle to an automotive maintenance shop if the warning light goes off and stays off.

In order to check the accuracy of the warning light bulbs themselves, each time the car is switched on the warning lights will appear for several seconds and then go off. This allows the motorist to do a quick visual check to ensure all the warning lights are working properly. If a bulb that usually lights up does not come on, simply replace that bulb.

If a warning light comes on and stays on, then most likely there's an issue with the indicated area which should be addressed by the driver or an auto maintenance professional. A repair shop or even a vehicle maintenance supply store will be able to diagnose the problem accurately using an OBD code reader. The code readers plug in to the vehicle's diagnostic system and tell the reader which sensor or sensors have been tripped. Because the reader can pinpoint what area of the vehicle is sending the code, the warning lights provide an accurate picture of what type of maintenance is required.

For more information about automotive warning lights and other related topics, follow the links below.

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  • EPA (Environmental Protection Agency). "On-Board Diagnostics: Frequently Asked Questions." Nov. 18, 2009. (Dec. 5, 2009)
  • Consumer Reports. "What to do if the "check engine" light goes on." March 2009. (Dec. 5, 2009)
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  • Yahoo Autos. "My Alternator Warning Light is On - What Do I Do?" (Dec. 5, 2009)
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